The invention relates to a process for preparing 1-amino-4-hydroxy-anthraquinones and to the use of the compounds thus prepared for mass coloration of plastics.
1-Amino-4-hydroxyanthraquinones are known, for example, as dyes for plastics and synthetic fibers and also as intermediates for preparing wool dyes. These compounds have hitherto been prepared by reacting 1,4-dihydroxyanthraquinone (quinizarin), optionally mixed with 2,3-dihydro-1,4-dihydroxyanthraquinone (leucoquinizarin), with amines in the presence or absence of condensation assistants.
In U.S. Pat. No. 1,931,264, for instance, bis-adduct formation is suppressed by use of an aqueous solvent, but at the same time excess amine is needed to obtain good yields. In GB-A 2,013,701, the reaction is carried out in the presence of surfactants. DE-A-161 96 46 and U.S. Pat. No. 2,419,405 describe the use of alcohols as a solvent.
Disadvantages common to all of these processes are the low space-time yield and the fact that the dye obtained is not sufficiently brilliant.
It is an object of the present invention to provide a process that is free of the disadvantages of the prior art.